With the rise of energy and transportation costs as well as increased concerns about greenhouse gas emissions, it is desirable to reduce the energy usage and carbon dioxide production associated with the manufacture of steel and cement, two of the quintessential construction materials of industrialized society, with the former used extensively in applications ranging from transportation to furniture. Current production techniques create steel and slag in one process with slag considered a waste byproduct having no meaningful value. A second and separate process is then utilized to grind the subsequently cooled slag for use as a filler with cement for the creation of a lower cost concrete. Locating both processes in a highly integrated manner at one industrial site such that the by-product of one is fed directly into the other minimizes a range of operating costs including the transport costs to a concrete plant. However, these previously separate processes can be modified such that the heat generated from the primary manufacturing process as embedded in the hot slag—which is typically wasted—is utilized to produce electricity (or mechanical shaft power) for sustaining both processes and for transmission, reducing the monetary cost and environmental impact of producing the materials while generating electricity that might otherwise come from the burning of fossil fuels. Thus, three industries—steel, cement, and power—can be impacted. Steel and cement are revolutionized, while the power industry is enhanced through the reduction of overall energy consumption and maximizing exergy efficiency on a kilowatt-hour basis.
Slag is the partially vitreous by-product of the smelting of metal ores. Its composition varies based on the ore being smelted, but it typically contains metal oxides and silicon dioxide. The smelting of iron ore in a blast furnace, an important step in the production of pure iron and steel, produces slag containing calcium oxide (CaO), silicon dioxide (SiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), iron oxides (FeO and Fe2O3), manganese oxide (MnO), and elemental sulfur (S); steel furnace slag, produced as a by-product of iron processing in a basic oxygen furnace or scrap steel processing in an electric arc furnace, contains all of the same compounds as well as phosphorous pentoxide (P2O5) and elemental iron (Fe). The cooling process affects slag structure and properties. Air-cooled slag is predominantly crystalline and has little or no cementitious properties, making it suitable primarily as a mineral aggregate. On the other hand, quickly quenching molten slag (such as with water) produces granulated slag, which is glassy and exhibits hydraulic properties (i.e., it hardens due to hydration). Thus, ground granulated blast furnace slag (GGBFS) is often referred to as “slag cement”, though the term can also be applied to mixtures of Portland cement and ground slag. Expanded slag is similar to GGBFS and is produced by treating molten blast furnace slag with controlled amounts of water, as currently known in the art, in various pit and machine processes, resulting in a material with cementitious properties between those of air-cooled slag and GGBFS dependent on the amount of crystallization.
Historically, slag was discarded as an essential waste of iron and steel production, at least until the beginning of the 19th century, when it became commonly used for construction in Europe. Since then, slag cement blends have demonstrated greater consistency, greater strength gains after setting, greater resistance to seawater and other chemical agents, reduced expansion, higher compressive and flexural strengths, and lower permeability compared to ordinary Portland cement (OPC). Because they are made of a recycled material, slag cements also reduce energy consumption and greenhouse gas emissions.
Olivine and serpentine are magnesium-iron minerals with the ability to adsorb (i.e., weakly bind) carbon dioxide (CO2) when heated to within a certain temperature window as known in the art. The carbonation reaction is an equilibrium reaction, such that the amount and rate of carbon dioxide adsorbed by the mineral is a function of both temperature and pressure. At supercritical pressures for carbon dioxide, a peak adsorption level occurs at approximately 200 degrees Celsius to 300 degrees Celsius, as known in the art. The carbon dioxide adsorption is an exothermic reaction. This unique property allows both minerals (olivine and/or serpentine, with the minerals in slag) to be utilized for carbon sequestration and/or carbon dioxide emissions avoidance respectively to combat global warming. By incorporating either or both of these minerals into a slag cement blend and heating the mixture during processing, the cement itself functions as a carbon dioxide reservoir, making the cement eco-friendly not only by recycling waste from steel production, but by allowing the removal and permanent storage (at least on a geological time line, as compared to “pumping” it into the ground) of additional carbon dioxide from the atmosphere.
WO 2006/123921 and US Patent No. US 2008/0168928 both titled “Concrete Composition Containing Atomized Steelmaking Slag And Concrete Blocks Using The Concrete Composition” by Oh et. al., discloses the production of atomized steel making slag balls to replace fine aggregates, preferably with a quantity greater than 30% replacement of known in the art fine aggregates. Furthermore, '921 utilizes slag balls created using “high-pressure gas mixed with water spray(ed)”. The utilization of water (understood to become water vapour) in the quenching process is fundamentally different than the disclosed invention which is preferably void of water vapour.
Furthermore, and importantly, the resulting atomized steel slag balls are also differentiated from the disclosed invention as the slag balls are a non-reactant filler for fine aggregates. '921 also does not enable carbonated materials to be incorporated at high levels in the resulting cement or concrete.
WO 2007/145384 titled “A Method For Stabilizing Slag And Novel Materials Produced Thereby” by Oh et. al., discloses a converter (of slag) refining process that utilizes high-speed oxygen to remove carbon saturated in molten iron via an oxidation reaction. Typically lime is utilized to supplement the inherent CaO. In the conventional treatment, a large amount of water is sprayed. The resulting free CaO (a.k.a. free lime) tends to produce calcium hydroxide (Ca(OH)2) when it contacts the sprayed water, is not desired for traditional Portland cement. '384 provides a method to minimize the generation of free lime that reduces/eliminates instability of converter slag that is caused upon cooling. One provision is a method for stabilizing slag that comprises and is dependent on molten slag to fall; subsequent injection of high-pressure gas to the falling molten slag to separate the molten slag into fine droplets; and finally quenching the fine droplets with the injected gas and surrounding atmosphere. '384 not only prefers the rate of mass flow rate of the slag (Jslag) to massflow rate of the injected gas (Jslag) to be in the range of 0.4 to 1.7 but specifically does everything possible to ensure the mass flow ratios to not exceed 1.7. One method of '384 to limit the ratio is by preferably utilizing water mist to the slag behind the area of gas injection. '384 also utilizes carbon particles having a sphere-equivalent diameter in the range of 30 to 150 micron injected into the falling molten slag, along with the injected gas (assumed to be containing oxygen, as carbon requires the presence of oxygen in order to oxidize into carbon monoxide or carbon dioxide). '384 discloses “on the other hand, if a greatly smaller amount of slag than the amount of injected gas is discharged, a treatment time is extended and consumption of gas increases excessively, resulting in inefficient and uneconomical treatment. Accordingly, it is essential to set an appropriate rate of discharge amount of slag/amount of injected gas.” Again, '384 does everything possible to avoid a mass flow ratio between slag and injected gas greater than 1.7, with specific concern of excessive consumption of gas. This is attributed to their energy consuming injected gas, as compared to the present disclosed invention that is net power producing.
'384 further limits the temperature to less than 1550 Celsius due to a “very fast linear velocity at an outlet of the nozzle, thus making it difficult to maintain desired quenching conditions suitable to restrict phase transformation”. '384 does anticipate the inclusion of additive for subsequent exothermic oxidation reactions to increase the slag temperature prior to atomizing. '384 does anticipate an increase in surface area, but is limited to the surface of the resulting slag balls and by explicitly blowing carbon powder along with the gas. This method is suitable only in the presence of oxygen, as an injection gas void of oxygen would simply lead to the carbon powder remaining on the surface of the atomized slag ball thus actually reducing the effective slag exposed surface area and not adding any surface porosity. '384 does further anticipate the utilization of a high mass flow rate of the injected gas, beyond their invention, to increase the surface area by first the creation of smaller particle size (100 micron or less) with subsequent agglomeration to a size of 1 to 10 mm. '384 is net energy consuming, as significant energy is required to produce high-pressure injection gas. '384 requires the molten slag to fall, as the discharged gas from the high-pressure injection gas is not utilized for any other purpose, thus the only objective is for the resulting atomized stabilized slag to fall via gravity. '384 further selects the injection gas from air, nitrogen, argon and helium, all of which have approximately less than 1% carbon dioxide. '384 further views the optimal size of the stabilized slag above the range of 200 micron to 5 mm, as the resulting stabilized slag is simply a replacement for fine aggregates and not a chemical reactant. '384 expansion of injected gas is effectively non-contained, and the slag is falling. '384 has low heat transfer rate, as the gas approximately immediately expands to atmospheric pressure. The injection gas at atmospheric pressure has a relatively low density and a comparably low coefficient of heat transfer. '384 specifically avoids the formation of free lime, and the absence of CO2 limits the formation of carbonates. Furthermore, the formation of carbonates is an approximately slow process due at least in part due to the low pressure of discharge gas (i.e., expanded injection gas) and low concentration of CO2.
U.S. Pat. No. 6,803,016 titled “Device For Atomizing And Granulating Liquid Slags” by Edlinger discloses a jacketed atomizing method that advantageously may be operated in a manner that the propellant jet is fed under supercritical conditions so as to cause its rapid expansion after having left the nozzle, by which the propellant jet is accelerated to supersonic speed. '016 utilizes a jet of combustion off-gases and (water) vapor as the propellant jet while, furthermore, gaseous hydrocarbons are also advantageously used as said coolant. When using these media, it is ensured at a comparatively low pressure that supercritical conditions and hence under-expanded media are fed to the respective nozzle, whereupon a rapid and vigorous expansion will subsequently occur so as to attain the desired supersonic speeds. The condensation of water from a propellant jet comprised of combustion off-gases and water vapor at a substoichiometric combustion results directly in a reducing gas CO+H2, a balance of CO2 that may be reused as a burning gas, to prevent the reoxidation of the iron powder.
In '016 both of the jets are able to impinge at supersonic speed creating a rapid and intensive comminution that is reached with a cloud forming subsequently, in which rapid cooling under a simultaneous rapid volume increase takes place due to the chemical decomposition of the cooling gas. The hydrocarbons of the coolant emerging in the sense of arrow are thereby reacted to CO and H2, said reaction with vapor leading to a doubling of the volume; since both media can be fed supercritically and, therefore, expand rapidly upon emergence from the nozzles, in particular the Laval nozzles, intensive comminution work and, at the same time, rapid cooling of the liquid slag, which leaves the slag outlet opening as a tubular jacket, are ensured. The coolant comprises gaseous hydrocarbons; the propellant jet is fed to the nozzle mouth of the lance under supercritical pressure, and the coolant is fed to the coolant nozzles under supercritical pressure. '016 is fundamentally different from the present disclosed invention through the utilization of water (vapour), does not increase the surface area or porosity of the resulting slag powder, and is not a net energy producer but rather is a net energy consumer for the creation of the supercritical cooling gas.
U.S. Pat. No. 6,082,640 titled “Method For Granulating And Grinding Molten Material and Device For Carrying Out Said Method” by Edlinger discloses a process for granulating and comminuting molten material in which the slag melt is acted upon by compressed water and discharged together with the vapour formed.
The published paper titled “The Basic Study on the Preparation of Steel Slag Cement with Gas Quenching Steel Slag” by Yue Long et. al., strives to utilize traditional gas quenching as a method to reduce free lime (CaO) through size reduction and reduction of crystallization time through relatively rapid quenching. Long et. al., is otherwise traditional cement composition without promoting subsequent chemical reaction in the resulting concrete composition.
Another published paper titled “High volume limestone alkali-activated cement developed by design of experiment” by Alexander J. Moseson et. al., discloses a cement comprising ground granulated blast furnace slag, soda ash (sodium carbonate), and up to 68 wt. % granular limestone. Another approach to ecological cement is that of geopolymer or alkali-activated cement (AAC), which generally use no OPC. Their advantages over OPC may include: (i) drastically less CO2 production; (ii) longer life and better durability; (iii) better defense against chemical attack (e.g. chlorides, sulfates); (iv) rapid strength gain; (v) better performance in marine environments. Moseson et. al., utilized As noted above, four raw materials were used. The first was slag (GGBFS) (St. Lawrence Cement, Camden, N.J.) with a Blaine fineness of 498 m2/kg (as tested by the authors per ASTM C204-07 [29]). Xray Fluorescence (XRF) analysis of the GGBFS was carried out by Arkema, Inc. in King of Prussia, Pa. (Table 1). Second is sodium carbonate, Na2CO3 (Brenntag Pacific, Inc., Santa Fe Springs, Calif.). Third is granular limestone with a CaCO3 content of 89.3 wt. % and a MgCO3 content of 10.7 wt. % (Oldcastle Stone Products, Atlanta, Ga.). The cumulative particle size distribution of the latter is: 23%<75 lm, 48%<150 lm, 68%<300 lm, 100%<1000 lm. Fourth, tap water. Moseson et. al., utilizes standard slag powder as produced by the energy intensive process of grinding GGBFS. This is differentiated by the present invention disclosure as the GGBFS preparation process is energy intensive (consuming power), has traditional reactivity due to moderately low (less than 500 m2/kg) surface area thus requires a higher utilization of slag for an equivalent cement/concrete strength.
In another prior art solution, for the purposes of stabilizing converter slag and reducing the amount of CO2 down to a level satisfying environmental restrictions, slag stabilizing techniques have developed for transforming CaO in converter slag into CaC03 via carbonation using CO2 gas that is blown to the converter slag, as disclosed in: 7th Conference of the European Ceramic Society of 2001, p. 879 (T. Takahashi and M. Fukuhara) [Key Engineering Materials, vols. 206-213 (2002) p. 879; Adv. Cern. Res., 12 (2000) p. 97 (T. Isoo, T. Takahashi, N. Okamoto and M. Fukuhara; Am. Ceram. Soc. Bull., 80 (2001) p. 73 (T. Isoo, T. Takahashi and M. Fukuhara); and Materia Japan, 39 (2000) 7 p. 594 (M. Fukuhara and T. Takahashi). Stabilized slag resulting from the above techniques has been proved to be eco-friendly. However, actually, the conventional techniques have a complex necessity for various troublesome facilities and technical processes such as crushing, compression, molding, etc., which are required for the fabrication of large-sized slag blocks. Accordingly, it can be said that the conventional techniques are impractical and uneconomical.
From AT 406 262 B a method for spraying oxidic slags became known, in which liquid slag was ejected from a tundish via a tundish tube, wherein a lance was introduced into the liquid slag to inject a propellant gas and, in particular, water vapor. The tundish tube provided in the slag outlet of the tundish as illustrated in AT 506 262 B could also be designed in the manner of a Laval nozzle, whereby vapor flow velocities in the supersonic range were observed, too, both due to the supercritical conditions under which hot vapor or water vapor was supplied and due to the subsequent possibility of a rapid expansion. In that known device a slag melt having temperatures of between about 1300° and 1500° C. was, thus, ejected using hot vapor as a propellant, rapid cooling having been effected subsequently within the cooling chamber by the reaction of carbon or carbon carriers with water vapor and the slag heat to carbon monoxide and H2, thus providing reducing conditions.
Thus, a need exists for a system capable of producing steel, slag cement, and electric power simultaneously while reducing the greenhouse gas emissions and overall environmental impact of all associated processes.